Warning! This synopsis may contain spoilers

The film starts with a man on an operating table with a massive wound in his abdomen. A surgeon comes in and tortures him by placing salt in his wound. The scene shifts to four friends, Tayler, Tony, Kai, and Nick, on a vacation. On their way home, they stop at a gas station where an alluring stranger named Diane asks for a ride to her truck, which has run out of gas. Nick agrees, but his girlfriend Tayler is suspicious. Nick drops her off at her truck, and Diane offers to get the girls some samples in gratitude. Diane then returns, wearing a gas mask and puts everyone asleep with nerve gas. The friends awaken to find themselves trapped in a house with a dozen other people. After a brief fight, Nick and Tony calm down and learn they have all been captured and the doors are locked. Everyone has a gadget inserted into his or her neck and they a projector playing a video of a woman telling them they have 24 hours to escape. By doing so they must inflict harm on each other using the weapons they've supplied with. Every bit of suffering fills up a bar and the bar is filled, they will be able to remove the gadgets and escape. If they fail the gadget will inject poison within their brains and kill them. One man, Julian, breaks down and removes his gadget and dies instantly. The others decide they have no choice and begin with Greg, a reporter who may know about this plan and hopes to see his son again. The group beats him and breaks off his fingernails, one girl, Tara, is especially violent and breaks his leg with a drill and Greg goes into a coma. Deciding they cannot risk injuring each other to that point, the group agrees to torture each person up to no higher than 6 percent of the meter in a certain order. After both Tony and Nick each take their turns also have their nails broken, Tayler who is next on the list, reveals she's pregnant. Tara insists she goes anyway but Nick volunteers to go for her. To help him get by, Tayler secretly gives Nick some medication pills, but this slows the meter. Next on the list, is a girl named Lisa, who tries to avoid it by hiding but is dragged out by Sam. . Later on, it is revealed to Greg that the group had earlier contemplated leaving Greg behind, as they'll need their strength to confront their captors. Everyone agreed except for Nick and Tony. Tony called everyone else cowards and Nick relays this to Greg who has now recovered. Tara insists that the majority opted to let Greg die, but Tony, fed up, punches her out and Greg is given the rest of the meds. Later, Tony, Tayler, and Lisa, then try to get six percent each by sticking their hands in boiling water but Kai backs down so Tony does his other arm. Meanwhile, Tara who has regained consciousness, takes a kitchen knife and tries to kill Tony for punching her. Tony is stabbed in the shoulder and falls with the pot of boiling water falling onto him. Tara is knocked out again this time by Nick, before she can finish Tony off. Tara is placed on the torture table, and upon regaining consciousness, Tony tells her that her actions raised the meter to 48%. Tara, somewhat nervous, urges them to get her shift done quickly, but Tony reveals they will be pushing higher than the usual six percent this time. Tara starts to protest that they had voted on six percent and breaks down in tears, begging to be released. She desperately tries to hold them back and in the process, cuts Kai, fatally wounding her. Tony, distraught and enraged tries to kill a helpless Tara but Nick convinces him to keep her alive. Tony agrees, but demands that he do what he wants to her. Tony severely damages Tara's larynx with a wrench, knocks out of a few of her teeth, removes some her skin with a grater, and cuts her arms open with a knife. When Tara finally passes out or dies, the meter is at 80%. After the others finish their torture, the meter fills up fully and the projector flashes a new message of the woman congratulating them and instructing them to place the vials in their gadgets in the door allowing them to escape. Soon only Greg and Tayler are left while Tony is unable to get back in. Suddenly Sam attacks Diane and Tony and is revealed to be the one who orchestrated this scenario. Nick pursues into the room seen at the beginning where Sam, having removed his gadget, locks Tayler up again. Greg admits to Tayler that he knew about this cult that feels everyone deserves pain and agony. Tayler tries to escape by inflicting burns on her back with an electric burner, pouring bleach on her already burnt arm, and slamming her injured arm in the cupboard door. Sam amused admits that he was one who had suffered injuries in his life and yet survived, believing, that everyone deserves pain to be innocent. Sam then activates a device that starts killing everyone except Nick who Sam sympathizes won't die for another ten minutes and yet assures him that Tayler won't be feeling any pain. Despite the poison, Nick is able to kill Sam with a screwdriver and takes some of the meds that he finds in the room, cancelling the poison. Nick rushes back to find everyone dead. Through heartbroken Nick leaves the room.

Days later, Nick is seen in a restaurant, his injuries treated, ordering waffles and cream. As he looks out the window, Nick spots Diane, hitchhiking with a redneck and goes after her, leaving money on the table. Hours later, Diane tries to "offer" the redneck a sample of her products, but he drives off. Diane, disappointed, heads back to her car, only to confronted by Nick, who slams her head against the car, knocking her out. Nick stuffs Diane in the back and puts on "Looks that Kill"on the radio and comments what Diane said earlier: I love this song.